1. Field of Art
The present invention relates to pull-type agricultural implements which are conceived for attachment to a pulling vehicle, and more particularly to implements having a pair of steerable wheels.
2. Description of Prior Art
Traditionally, agricultural tractors have been designed for low road speeds, not exceeding 25 km/h. However, more and more modern tractors are capable of attaining top speeds of 50 km/h without discomfort to the user or danger for the tractor structure. In practice however, the speed of the tractor still has to be limited because the implements attached to the tractor do not allow high speeds. This certainly is the case where no suspension is provided for the wheels of the implement.
Accordingly, adequate suspension systems have been fitted to pull-type implements, permitting road speeds in excess of 25 km/h for the whole tractor-implement combination. In one embodiment the implement has been provided with a kind of bogie which is attached by two sets of leaf springs to the frame of the implement. The bogie comprises four wheels mounted to a front and a rear axle. Such structure behaves satisfactorily during road travel, where large turns are to be made, but seriously hampers the operation in the field, where the implement sometimes must take very short turns. The second pair of wheels then seriously hampers the movement of the baler and may even deteriorate the earth on headlands.
In response thereto it has been suggested to make the rear wheels of the implement steerable such that they can adapt freely to the short turns. However, for road travel all wheels have to be held in a fixed position to keep the wheels from fluttering in an uncontrolled movement, especially at high speeds. Moreover, the free movement of the rear wheels may complicate the rearward movement of the implement, as the wheels tend to turn over and deviate the implement to the left or right.
Hence there is a need for means disabling the free movement of the steerable wheels.
According to one aspect of the present invention there is provided an agricultural implement, comprising a main frame and a hitch attached to the main frame for attaching the implement to a towing vehicle. There are a pair of steerable wheels supporting the main frame and a means for blocking the steerable wheels in a fore-and-aft direction. The hydraulic circuitry for controlling functions of the implement comprises a feed line and a return line for connection to a hydraulic pump and an oil tank respectively, the connection enabling normal operation of said functions. Finally the circuitry comprises a means for actuating said blocking means by providing hydraulic pressure from said pump to said return line.
According to another aspect of the present invention, there is provided a method for blocking steerable wheels on an agricultural implement. The implement having a main frame, a hitch attached to the main frame for attachment of the implement to a towing vehicle and a pair of steerable wheels supporting the main frame. There is a means for blocking the steerable wheels in a fore-and-aft direction consisting of hydraulic circuitry for controlling functions of the implement. The circuitry comprising a feed line and a return line for connection to a hydraulic pump and an oil tank, respectively. The method comprising the step of actuating said blocking means by providing hydraulic pressure from said pump to said return line.